The embodiments of the present invention relate to the field of a liquid crystal display, and to a shift register and a gate-line drive device therefor.
In recent years, products of liquid crystal display (LCD) are developing very fast, more and more thin film transistor liquid crystal displays with high quality are put to the market, its application fields are constantly expanded.
The pixel array of the liquid crystal display comprises interlaced several rows of gate scan lines and several columns of data lines. Wherein, the gate-line drive device consisted of several shift registers provides signal for the several rows of gate scan lines of the pixel array.
The increase of ON voltage of the thin film transistor directly relates to the voltages on both terminals of gate and source, the greater the voltages on both terminals of gate and source, the longer the time for applying the voltage, and hence the bigger the increase of the ON voltage. FIG. 1 is a relationship diagram illustrating the relation between the ON voltage shift and time with the thin film transistor constantly under the gate bias voltage. As shown in FIG. 1, the vertical direction represents the ON voltage of the thin film transistor, the horizontal direction represents the time during which the voltage is continually applied. It is noticed from the figure that, if the voltage is constantly applied to one thin film transistor, then the ON voltage of the thin film transistor will constantly increase, at the end causing the thin film transistor unable to be turned on, eventually causing the circuit inoperative.
In a shift register, the duty ratio of silicon thin film transistor is relatively large, basically between 5%-10% or even more. Under the positive bias voltage for the gate, the operation current of the thin film transistor will drop, and the shift of the ON voltage becomes higher and higher, eventually preventing the thin film transistor from normal operation, thus the stability of the shift register is affected.